LNB – Low Noise Block

LNB (Low Noise Block Down Converter) A device mounted on the dish, designed to amplify the satellite signals and convert them from a high frequency to a lower frequency. LNBs can be controlled to receive signals with different polarisation. The television signals can then be carried by a double-shielded aerial cable to the satellite receiver while retaining their high quality. A universal LNB is the present standard version, which can handle the entire frequency range from 10.7 to 12.75 GHz and receive signals with both vertical and horizontal polarisation. The most commonly used LNB is actually called LNBF, the F standing for Feedhorn (inbuilt).An LNB can be either single (one output), Twin (two outputs), Quad (four outputs), Quatro (four outputs), or Octo eight outputs).

A Twin LNB would be required when more than one receiver is used, allowing the viewing of different channels on two independent satellite receivers. Twin output LNBs are required for Freesat+ and Sky+HD receivers, allowing you to record two programmes at the same time, or record one while watching another. Low noise block converters have a hard life; they operate in extremes of temperature and humidity, and although they generally have a very low failure rate they do not last forever. Some fail as they get older, others suffer a drop in performance, resulting in poor picture quality, replacing an old LNB could improve reception.

Universal LNB

A universal LNB can receive both polarisations and the full range of frequencies in the satellite Ku or C band. Some models can receive both polarisations simultaneously through two different connectors, and others are switchable or fully adjustable in their polarisation.Here is an example of Universal LNB specifications:Local oscillator (LO): 9.75 / 10.6 GHz. Frequency: 10.7–12.75 GHzNoise Figure (NF): 0.5 dBPolarization: Linear

LNBF – Low Noise Block Feedhorn

Direct Broadcast Satellite (DBS) dishes use an LNBF (“LNB feedhorn”), which integrates the antenna’s feedhorn with the LNB. In the case of DBS, the voltage supplied by the receiver to the LNB determines the polarisation setting. With multi-TV systems, a Twin LNB allows both to be selected at once by a switch, which acts as a distribution amplifier. The amplifier then passes the proper signal to each receiver according to what voltage each has selected. LNBFs should never be used on Prime Focus dishes, this always results in extremely poor performance.

Noise Figures

Theoretically, the lowest noise figure obtainable from any device is limited by any components in the signal chain with the highest thermal noise. The first component in the chain would be the detector circuit and on a Universal LNB, this would be a pin diode. At Ku band, the detectors are rated at manufacture to about 40K which converts to a figure of 0.5 dB. Presently the LNB market is active by those selling what appears to be an extraordinarily good device, some use the best of the component batch – and end up with good performance overall (rare). Some modify existing LNBs by the use of fancy smoothing circuits to eliminate any further incoming noise from the power supply – there are definite improvements when used with cheaper receivers, especially those with switch mode supplies.

The LNB sets the noise floor for your entire satellite receiving system. Less noise here means that more signal will actually arrive at the receiver. Today’s high-performance LNBs use Gallium Arsenide (GaAs) semiconductor and High Electron Mobility Transistor (HEMT) technologies to minimize the noise level of the LNB. Note even the best LNB will only marginally improve reception, the only way to significantly improve reception (Gain), is to use a larger dish.Read more about LNB specification

LNB Skew

Skew refers to the angle of the LNB relative to the rest of the dish, you are maximising the gain of the LNB.This could be the difference between a good watchable picture or poor reception.All geostationary satellites are located above the equator (the Clark Belt).

They are placed here to match the rotation of the earth. Inside a satellite’s footprint, LNB skew is not all that important, however as you approach the fringes of the signal footprint it becomes ever more crucial to getting good reception. The LNB is kept in place by either a screw or a nut.

Loosen these and it will be possible to rotate the LNB left or right. The degree of tilt varies depending on your location.The satellite appears to be tilted as viewed from Earth, this means the LNB has to be tilted to a similar angle so that it matches the geometry position of the satellite. The degree of tilt varies depending on both your location and on which satellite you want to receive.Skew varies from about 15º in the north of Scotland to around 22º in the south west of England, always rotate clockwise as viewed facing the front of the dish.

Most commercial satellite dishes have a certain amount of skew built in, the LNB will appear to be lopsided.In areas where the signal is strong, skew is not such an issue, once outside the main reception area as with Astra 2D overseas, skew becomes important.The LNB is locked in place by either a screw or a nut. Loosen it and the LNB will rotate in its housing. Rotate it one way or the other until the signal quality is maximised.

Inline Amplifiers

Inline amplifiers will not increase weak signals, infarct they will probably reduce the signal even more. An Inline Amplifier should be used when the cable run from the LNB to the receiver exceeds 75 – 100 feet; install the amplifier between the LNB and the Multiswitch or satellite receiver.

Inline amplifiers are powered by the voltage already present on the satellite signal coax. If your signal is not strong enough in the first place, you are really only amplifying noise. An Inline amplifier is unfortunately of little or no use when trying to increase a weak signal, it will also ‘boost’ stronger signals swamping your already weak signal. A better LNB or larger dish will give far better results.Increase your dish size and use a good receiver with a low threshold.

C120 LNBs

C120 LNBs do not have a feedhorn in the same way as LNBFs, a feedhorn preferably one from the manufacturer of the LNB, has to be attached to the LNB. C120 LNB’s should be used on offset dishes larger than 1.2m metres, though with an offset feedhorn. They will almost always produce superior performance than a LNBF, particularly when using Invacom C120 LNB’s. Other makes such as MTI C120 perform very poorly in these circumstances.

Feedhorns

The most common type of feedhorn manufactured today is called a scalar feedhorn. This type of feed has a large circular plate with a series of three or four concentric rings attached to its surface. The scalar rings conduct the incoming signal from the outer edges of the focal cloud to the large waveguide opening located at feed centre.
The scalar feedhorn primarily sees or illuminates the inner portion of the antenna’s surface area, while attenuating the signal contribution from the outer portion of the dish by 8 to 22 dB, depending on whether the dish is deep or shallow in its construction.

Molecular motion within the Earth itself generates random noise which permeates the entire electromagnetic spectrum used for the transmission of satellite signals. This random noise is many times stronger than the satellite signals reaching any location.

The attenuation or illumination taper provided by the feed sharply reduces the reception of the Earth noise which lies just beyond the antenna’s rim.
The outer area of the antenna’s surface, therefore, acts more like an Earth shield for the feedhorn than as a contributor to the overall signal gain of the receiving antenna.

Invacom C120 Quad QDF-031

The Invacom C120 Quad QDF-031 is probably one of the best LNBs to use in areas where the signal is weak (fringe reception), used in conjunction with a quality feedhorn such as the Raven Andrews feedhorn (Channel Master), it gives excellent results on both horizontal and vertical transponders.A high-performance universal LNB with 4 independent switched outputs. Typically used to supply 4 receivers, for dishes supplied with their own feed-horn.

Typically used with large dishes, where the signal strength is poor, ideal for reception of Astra 2E and Astra 2F outside the UK, cheaper LNBs are fine for viewing in the British Isles.Please note, the best way to increase gain, is to use a larger dish, a good LNB will only marginally increase gain.Input Frequency – 10.7 – 12.75 GHzOutput Frequency – 950 – 2150 MHzNoise Figure – 0.3dB typicalGain – 50 – 60dBInterface – C120 flange, 18.5 ØIdeal dish F/D – N/A

It seems to be pot luck buying an MTI, and one is left wondering if they really do rigorously test and select their top of the range LNBs? The older Bluelines perform better than the older Greyline models such as the AP8-T2.MTI use to have a very good reputation, their older Blue Line LNBs performed very well for a reasonable price. Recent ranges such as their High Line and Supreme Lines perform much worse.

Probably the best MTI model to use in fringe reception areas are the MTI AP8-T2B, AP82-T2B and AP84-T2B, these performed very well on vertical transponders and quite good on horizontal ones. These all had a noise figure of 0.6dB.

The MTI AP82-T2FBL Supreme Line, which has a noise figure of 0.2dB performs very well on horizontal transponders and poorer on the vertical, this could be useful depending on where you live. East of the British Isles, vertical transponder are mostly stronger than the horizontal ones.Avoid the MTI High Line AP8-T2NRC 0.2dB, these perform badly in fringe areas, though they are fine for use in the British Isles.

Smart Titanium LNBs from Germany have had some quite good reports and there are many in use overseas. The Smart Titanium 2nd Edition TQSG with a noise figure of 0.2dB, is very biased towards vertical transponders, giving very good results. The same can not be said for horizontal reception. A good LNBF if used in the British Isles for reception of Astra 2F, it could give reception problems overseas.The Smart Titanium TQS with a noise figure of 0.1dB, performs very similar to the MTI AP82-T2FBL, biased towards horizontal transponders and average results on the vertical transponders.

It is claimed that the expensive Syntec 2000 can greatly improve reception with its low noise level of 0.3dB. The Astra 2 website has carried out its own tests, read & received reports that do NOT back up this claim. The improvement in signal gain is marginal, the only real way to improve signal gain is to increase dish size.The Syntec 2000 LNB appears to be ‘biased’ toward High Band reception, consequently suffering a loss of Gain in the Low Band frequencies (0.8dB typical).

Also, it appears to have a tendency to be oversensitive to the 22kHZ tone output from certain receivers, causing an inability to discriminate between High and Low Band, on certain of the lower frequencies.

The net result being, that the LNB remains active in High Band when the receiver has selected Low Band.Performance aside, one thing is certain, they are overpriced, and perform no better than far cheaper models. There are many sites which advertise these as being high quality, with a very low noise figure and ideal for use overseas, or where maximum dish size cannot be increased. Not recommended, due to both performance and the high cost.

Inverto LNBs

The Inverto Silvetech LNBs, with a noise figure of 0.3dB, seem to perform better than the Whitetech range, with a noise figure. Inverto Silvertech LNBs seem to perform better than the Smart Titanium according to some reports on the Internet.Test carried out by Snap in Madrid on Astra 2D, using an Inverto C120 Whitetech single LNB, gave the following results:

Tested an Inverto C120 white tech single on my dish in Madrid this week, with a surprising result. At 00.45 CET, the Invacom Quad C120 fitted on a Prodelin 180 cm dish gave the following on a Lacuna/Wolsey Mk3 meter:- TP 45 10773 H …signal quality of 4.75 or 50 numeric TP 46 10788 V… signal quality of 6.5 or 68 numeric TP 4 11778 V ( Sky default transponder) 7.5 or 78 numeric The Inverto had values of:- TP 45 10773 H … signal quality of 3 numeric 32 TP 46 10788 V… signal quality of 6.5 numeric 68 TP 4 11778 V … signal quality of 7.5 numeric 77 The threshold of picture breakup is around a value of 4.5 using a Pace TDS 470 n, Pace 430n or Thomson HD. The threshold is slightly better, a value of 4.25, on a Pace 2600 CI. This value is shown on the meter by a number of bars on a scale of 1 – 10, with 10 being maximum. The second value is a number on a scale of 0- 99. What do these values mean in the real world? The Invacom was delivering a perfect picture on both BBC transponders. The signal on 10773 H was just above the threshold at which a picture will start to show break up, with BBC 2 BBC 3 and BBC 4 all received flawlessly. The Inverto gave a perfect picture on TP 46. TP 46 carries BBC One regions. TP 45 was only just about locking and showed ‘no satellite signal being received’ on the receiver, tuned to BBC 2. Conclusions: the Inverto is very good on vertical 2D transponders and is an inexpensive alternative to the Invacom. It would be a poor choice in territories such as Spain and Portugal, as the LNB’s horizontal polarity performance is poor. It is the smallest LNB on the market, quite useful for some dishes such as the Gibertini 1.2 and 1.5, which has an inadequate mounting bracket for large LNB/feedhorn combinations such as Invacom/Channelmaster, which tend to tilt backwards when fitted to these dishes. This test was carried out on the Astra 2D satellite which is no longer in service at 28.2° East.